This application pertains to the art of adjusters and, more particularly, to adjusters for movable mechanisms which can be tightened or loosened. The invention is particularly applicable for use on vehicle brakes and will be particularly described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used for adjusting other movable mechanisms.
Automatic adjusters for automobile brakes commonly operate only to tighten the brakes when they become too loose. In many situations, such as when the brake drums expand after heavy braking, the brakes will automatically adjust in accordance with the increased diameter of the drums and will be too tight when the drums cool. This causes an unnecessary and undesirable drag on the vehicle, and causes unnecessarily rapid wear of the brake linings.
Known brake adjusters include the type disclosed in U.S. Pat. No. 2,998,104 issued Aug. 29, 1961, to McClure et al. This adjuster includes a rack for driving a rotatable ratchet wheel in one rotatable direction during overtravel and undertravel of the brake mechanisms. The ratchet wheel is axially shiftable, and is clutchable to one of two pulleys. During overtravel of a cylinder in the brake system, pressure operates a clutch for engaging the ratchet wheel with the pulley for tightening the mechanism. A spring biases the ratchet wheel into engagement with the other pulley after the mechanism has been tightened and rotation of the other pulley loosens the mechanism. The use of a clutchable ratchet wheel operated by a cylinder makes the adjuster very complicated.